1. Technical Field
This disclosure relates to a liquid crystal display (LCD) device and a liquid crystal composition used therefor.
2. Description of the Related Art
A liquid crystal display device may include a first substrate having a plurality of pixels, a second substrate, and a liquid crystal layer which is interposed between the first and second substrates. The liquid crystal display device changes a transmittance ratio of light in the liquid crystal layer according to an electric field generated between each of the pixel electrodes and a common electrode, thereby displaying an image. The liquid crystal display device may include a plurality of pixels each of which may include a pixel electrode.
Recently, investigations have been made to display not only a 2D image but a 3D image by using the liquid crystal display device, and there has been a need for a solution which provides more image information to a user. Therefore, there is a need for a liquid crystal display device which has a high driving speed as well as higher reliability, when compared with conventional liquid crystal display devices.
As disclosed herein, an exemplary embodiment provides a single liquid crystal compound with high dielectric anisotropy and high refractive index anisotropy as well as improved low temperature stability, and a liquid crystal composition comprising the same.
Another exemplary embodiment provides a liquid crystal display device comprising the liquid crystal composition with high dielectric anisotropy and high refractive index anisotropy as well as improved low temperature stability.
According to an embodiment a liquid crystal display device comprises a first substrate, a second substrate which faces the first substrate, an electrode part which is provided on at least one of the first substrate and the second substrate, and a liquid crystal layer which comprises a liquid crystal composition and is provided between the first substrate and the second substrate.
According to an embodiment, the liquid crystal composition comprises at least one liquid crystal compound represented as Formula 1.

In Formula 1, R1 represents hydrogen or an alkyl having 1-15 carbon atoms, in which at least one —CH2— group may be independently replaced by —C≡C—, —CF2O—, —CH═CH—, —O—, —CO—O—, —O—CO— or —O—CO—O— in such a way that no oxygen atoms bind to each other, and 1-3 hydrogen atoms may be replaced by halogen atoms,
R2 represents —F, —Cl, —CF3, —CHF2, —CH2F, —OCF3, —CN, —NCS, or an alkyl having 1-5 carbon atoms substituted with one to three of —F, and —CH2— groups are optionally replaced by O atoms independently of each other, in such a way that no two oxygen atoms bind each other,
(F) represents that a hydrogen atom is optionally replaced by —F, A11, A12, A13, A21 and A22 represent one of the following structures independently of each other:
Z11, Z12, Z13, Z21 and Z22, may be each independently a single bond, —CH2CH2—, —CH═CH—, —CH2O—, —OCH2—, —C≡C—, —CH2CF2—, —CHFCHF—, —CF2CH2—, —CH2CHF—, —CHFCH2—, —C2F4—, —COO—, —OCO—, —CF2O—, or —OCF2— independently of each other, a, b, c, d and e are each independently an integer from 0 to 3, and a+b+c+d+e is less than or equal to 5.
According to an embodiment, at least one of Z11, Z12, Z13, Z21 and Z22 may be —CF2O—.
According to an embodiment, d and e are 0, and R2 may be —F, —OCF3 or —CF3.
According to an embodiment, Z13 is —CF2O—, d and e are 0, and R2 is —F, —OCF3, or —CF3.
According to an embodiment, the liquid crystal compound of Formula 1 may be represented as Formula 1-1.

R1, R2, A11, A12, Z11, Z12, a, and b are the same as in the definitions for Formula 1.
According to an embodiment, the liquid crystal compound of Formula 1-1 may be represented as Formula 1-2.

R1 is the same as in the definition for Formula 1, and o is 0 or 1.
According to an embodiment, the liquid crystal composition may further comprise at least one liquid crystal compound represented as Formula 2.

R11 is the same as in the definition for R1 in Formula 1, R21, in addition to the definition of R1 of Formula 1, represents —F, —Cl, —CF3, or —OCF3, A3 and A4 are 1,4-cyclohexylene or 1,4-phenylene, independently of each other, and A5 represents one of the following structures:

According to an embodiment, the liquid crystal composition further comprises a liquid crystal compound which is represented as Formula 3.

R11 and R12 are independently the same as in the definition of R1 in Formula 1, and A3 and A4 are independently 1,4-cyclohexylene or 1,4-phenylene.
According to an embodiment, the liquid crystal composition may further comprise a liquid crystal compound which is represented as Formula 4.

In Formula 4, R1 and R2 are the same as in the definitions of R1 and R2 in Formula 1, A11, A12, A13, Z11, Z12 and Z13 are also the same as in the definitions of A11, A12, A13, Z11, Z12 and Z13 in Formula 1, f, g, and h are each independently 0 or 1, and f+g+h is 2 or 3.
According to an embodiment, the liquid crystal composition may further comprise at least one liquid crystal compound which is represented as any one of Formulae 5-7.

R1 and A11 are the same as in the definitions for Formula 1, p is 0 or 1, R3 represents hydrogen, oxygen radical, or an alkyl having 1-15 carbon atoms, in which at least one —CH2— group may be independently replaced by —C≡C—, —CF2O—, —CH═CH—, —O—, —CO—O—, —O—CO— or —O—CO—O— in such a way that no two oxygen atoms bind to each other, one to three hydrogen atoms may be replaced by halogen atoms, n is 1-12, and m is 0-12.
According to an embodiment, the liquid crystal composition further comprises a pitch modifying agent which is represented as Formula 8.

R1 is the same in the definition for Formula 1.
By preparing the liquid crystal composition according to the present disclosure, a liquid crystal composition which has improved low temperature stability as well as a high dielectric constant and a high refractive index, may be manufactured.
Also, by preparing the liquid crystal composition according to the present disclosure, it is possible to provide a liquid crystal composition which is optimized for various modes of liquid crystal display devices such as e.g., twisted nematic (TN), super twisted nematic (STN), in plane switching (IPS), fringe field switching (FFS) or plane to line switching (PLS), etc.